Correct wheel and chassis alignment is critical to a vehicle's handling performance, as it allows the tire contact patches to work effectively through all phases of suspension motion. Each vehicle, and indeed each individual driver, will have a preferred alignment set-up depending on the application and conditions. Vehicle wheel alignment is particularly important in racing applications, where small changes in alignment can have a dramatic handling impact on highly responsive race cars. However proper wheel alignment is important for all vehicles, such as racecars, trucks, cars, airplanes, trains, motorcycles, go-karts, mopeds. The present invention can also be used for aligning the treads on bulldozers, tanks, and snowmobiles and can be used for aligning a variety of other components.
Most commercial automobile and truck service stations, and also many well-funded race shops, used sophisticated wheel and vehicle alignment systems. However, those systems are extremely expensive, and are not readily obtainable by the average race team or to the do-it-yourself mechanic. Moreover, because those sophisticated alignment systems are not portable, even well-funded race teams must find an alternative for changing and measuring vehicle alignment at the racetrack.
A standard portable method for setting alignment is commonly referred to as the "string method." In accordance with the string method, the vehicle to be aligned is placed on jack stands to allow easy access to its underside on a known flat and true surface. First, the centerline of the vehicle must be determined. To determine the centerline, two identical points called pick-up points are located on both sides of the rear and front of the vehicle. For example, identical bolts on the suspension system can be used. Then a plumb bob is dropped from each of the four inner suspension pick-up points and points are then marked on floor or surface under the plumb bob. The mid-way point between the two front marks and two rear points are measured and marked on the floor. The two midway points are then connected with a string, or centerstring, that extends past the chassis to establish the centerline of the vehicle. Two points are then scribed or marked on the underbody of the vehicle to provide a future reference of the vehicle's center line. To determine the points to be scribed, a plumb bob is dropped from a convenient point on the chassis so that the plumb bob is aligned with the centerstring. The vehicle is then lowered to the floor. Next,two jack-stands, having a string strung taut between them, are set up on both sides of the vehicle. Each set of jack stands and string are set to within approximately six inches of the wheel rims and at approximately the same height as the axle. The distance between each string and the center-line is measured at both the front and rear of the vehicle. The jack stands are then adjusted until the front and rear measurements are equal. When this is accomplished, the strings on the outside of the vehicle are set parallel to the centerline of the vehicle, and provide a reference line for making alignment measurements.
To determine front or rear "toe" (also called "tracking" in some countries), using the string method, a machinist's ruler is used to measure the distance from the string to the front edge of the wheel rim. Next, the distance from the string to the rear edge of the wheel is measured. If the rear edge measurement is smaller than the front edge measurement, toe-in is present. If the rear edge measurement is larger, toe-out is present. The toe is then adjusted and measurements retaken until the desired results are obtained.
In some instances, the race mechanic will mark at least two points closer to each side of the vehicle that define a line that parallels the centerline of the vehicle. With many stock cars, the side frame rail can be used as that line. By using these two points on the vehicle, the mechanic does not have to crawl under the car to set up the centerline. Instead he merely has to determine that the strings on both sides of the vehicle are parallel to these two points on the vehicle.
For cars with an independent front and rear suspension, the toe of both the front and rear wheels can be determined. Whereas only the front wheels of a car with a live axle can be adjusted for toe and the rear wheels normally should parallel the centerline of the vehicle. For cars with a live rear axle, a similar method may be used to determine whether the centerline of the axle is properly aligned with the centerline of the car. Since the rear wheels on a live rear axle should parallel the vehicle centerline, measuring the "toe" of each tire will determine whether the centerline of the rear axle is properly aligned with the centerline of the vehicle. In this case, the "toe" measurements on both rear wheels should equal zero which shows that the centerline of the live rear axle is perpendicular to the centerline of the car.
Although the string method has long been the standard for obtaining toe measurements in the field, it has several drawbacks, especially for use in high-speed racing applications. First the string method is not very accurate or repeatable. In racing applications, wheel alignment must be correct and repeatable, and is often changed several times in a single weekend. To make accurate alignment measurements, it is necessary to roll the vehicle forwards and backwards several feet to set and load the suspension before taking the measurements. In the string method, the strings are carefully set with the car in a specific and stationary position relative to the centerline. Thus, any subsequent movement of the vehicle will require that the strings be reset. If the strings are not reset, or if the vehicle is not rolled forward and backward between alignment adjustments, inaccuracies in measurement and alignment will result. Second, the time necessary to set up the strings in the string method is significant. Thus, it is not practical to "re-string" the car for alignment checks between short test or qualifying sessions. Third, the string method is difficult and time consuming for two mechanics to perform, and is even more difficult for someone acting alone. Each of these drawbacks makes the string method useful only as a last resort. Thus, the need has long existed to develop alternatives to the string method of vehicle alignment.
Several alternative wheel alignment systems make use of visible lasers or beams to replace the strings that are used in the string method. For example, U.S. Pat. No. 4,466,196 to Woodruff uses a laser and a sensor module and that are both secured to their respective spindles of the vehicle's wheels by means of a magnet. The sensor module and the laser housing each have the ability to rotate. However, mounting and setting the sensor modules and laser housing can be time consuming, and can be difficult as well depending on the configuration of the wheel rim or tire spindle. In addition, if the laser sensor and laser housing is not secured properly or consistently, erroneous measurements can result. Lastly, because the laser housing and module are constructed as a single piece, the laser can only be used for the single purpose of vehicle wheel alignment, and cannot be easily adapted or removed for other purposes.
U.S. Pat, No. 4,578,870 to Cooke has the capability of projecting a laser plane by using a switching mechanism and a cylindrical lens that changes the beam of light typically emitted by a laser into a plane of light. The system is primarily designed for the inspection of vehicle frame and body alignment, and is preferably employed with a vehicle frame and body system, such as mounting carrier bars to the body of the vehicle for which to attach the laser generator and respective target, or possibly some other type of external framework assembly designed for the purpose of mounting the laser generator and target. The '870 patent incorporates the use of two elongate carriers bars that are mounted to the body of the vehicle orthogonal to the vehicle's center line. The laser beam plane generator is mounted on one of the bars, and the target is mounted on the other bar. Because the device can project a vertical laser plane that is projected on all surfaces within the plane, it is not necessary to rotate the laser beam plane generator to sight in the individual targets. It therefore creates a plane orthogonal to its elongate mounting bars of the vehicle frame and body alignment system. However, because of its design, it still requires some time to set up. The set up time will vary depending upon what type of vehicle and alignment system is used with the beam/plane projection laser. At the very least, the alignment system must be mounted on the vehicle (such as the two carrier bars), or an external system must be set up. The beam/plane projector and respective targets must then be mounted to the alignment system and adjusted. In addition, because it is designed to be used with the elongated carrier bars, it is complicated and appears to require considerable set up.
There are other patents, such as U.S. Pat. No. 4,598,481 to Donahue, that incorporate the use of laser generated planes for vehicle alignment purposes. However, the laser generated planes typically require the use of an elaborate frame structure for which to mount them and their corresponding targets, therefore restricting their portability and use in other measurement type applications. Numerous other vehicle alignment systems exist that use a visible laser to provide a reference line for making measurements. See, for example, U.S. Pat. Nos. 5,274,433 and 5,048,954 to Madney et al., U.S. Pat. No. 4,330,945 to Eck, and U.S. Pat. No. 3,962,796 to Johnston.
The applicant himself also has made and sold several laser-based vehicle alignment and measurement devices, including: U.S. Pat. No. 5,600,893 to the applicant for "A Process and System for Measuring Alignment of Automotive Vehicle Suspension" that is used to measure bump-steer, toe, and camber; an updated version a laser toe angle gauge to be used on go-karts, snowmobiles ATV's etc. . . . ; and a laser system used to accurately measure race car chassis'to help determine if a race car is within the required specifications.
The toe and camber measuring device of the applicant's '893 patent consists of a pivotal laser light source, a reflector, and gridded target that are positioned in a straight plane that extends from the wheel hub axis. The pivotal light source is positioned so that the projected laser beam is directed at the center point of a magnetically mounted reflector. The reflector is located on the flat surface of the rotor brake and is orthogonal to the wheel hub axis. The laser beam reflects off the reflector to the gridded target area located at least sixty inches behind the pivotal A light source. A mark is made on the target at the point where the laser beam strikes it. this initial mark is typically done with the car raised to a height equal to the radius of the tires to be used with the vehicle. The position of the suspension system is then changed by either raising or lowering the suspension in one inch increments. At each increment a mark is made on the target that corresponds to the beam spot. The change in toe is represented by any horizontal movement of the reflected light beam. The measured distance between the marks correlates to a change in the position of the reflector as the vehicle is raised and lowered. This measured distance is then use to determine the amount of toe travel by use of a conversion chart. Camber angle change is determined in the same way, only the distance measured will be on a vertical plane. The camber angle change is then derived using another conversion chart. Using this procedure can produce results that are accurate to one millionth of an inch. The procedure, however, requires the use of only laser line technology, a pivotal mounted light source, a reflector, and a griddled target for which to measure distance.
The Laser Toe Gauge for go-karts operates on the same premise as above by using a laser beam, reflector, and target. In addition there is an angle indicator incorporated into the laser head. Instead of a single mirror or reflector, it uses a rail that is mounted to one of the front tires and extends longitudinally towards the front of the kart with a mirror surface at its end parallel the body of the kart. On the opposite front tire, the laser rail is mounted and extends longitudinally to the front of the kart where the laser head is mounted and parallel to the body of the kart. The laser is turned on and the laser reflection is adjusted with an angle adjustment knob until the reflected beam hits the laser target or scribe line that is mounted on the front of the laser head. The toe angle is then read from the angle indicator.
The axle and frame laser alignment system also works in much the same way. It incorporates the use of two separate mirrors and a laser rail housing with a slidable laser head. The two mirrors are mounted at selected points on one side of the vehicle. To measure axle alignment, one mirror would be positioned on the frame of the vehicle and the other would be mounted parallel to the first mirror on the end of the vehicle axle. The rail housing is positioned directly in front of the mounted mirrors. The laser head is then slid into position directly in front the mirror that is mounted to the vehicle frame so that the beam reflects into the center scribe line on the front of the laser head. The laser head is then moved along the linear rail to the mirror mounted on the axle of the vehicle. The rear axle is then adjusted until the beam reflects onto center scribe line on the front of the laser head.
The need still exists, however, for a simple alignment measuring system and method that is easy to set up, accurate, repeatable and universal in application across different types of vehicles.